Field of the Invention
The present invention relates to a rectangular secondary battery.
Description of Related Art
Non-aqueous electrolyte secondary batteries, typified by lithium-ion secondary batteries, are used in hybrid automobiles, electric automobiles, large-scale electricity storage systems, and the like. Preferably, the non-aqueous electrolyte secondary batteries have rectangular shapes so that the space efficiency or the cooling efficiency of the batteries can be improved.
In such a rectangular secondary battery, a planar electrode body and a liquid electrolyte are disposed in a rectangular housing. In general, the housing is made of a metal. In order to prevent direct contact between the housing and the electrode body, an insulation sheet is disposed between the housing and the electrode body.
For example, Japanese Published Unexamined Patent Application No. 2009-170137 (Patent Document 1) discloses that a planar electrode body, which is to be disposed in a metal housing, is wrapped in an insulation sheet that has been folded into a box-like shape. Japanese Published Unexamined Patent Application No. 2009-048966 (Patent Document 2) discloses that an electrode body, which is to be disposed in a housing, is wrapped in an insulation film having a bag-like shape.
Patent Document 2 also discloses that a gap between the housing and the electrode body is filled with a gap filling member, which is a member independent from the bag-shaped insulation film.
It is necessary to flexibly change the thicknesses and the areas of a positive electrode plate and a negative electrode plate of a rectangular secondary battery depending on capacity and characteristics required for the battery. Accordingly, it is also necessary to flexibly change the thickness of a planar electrode body, which includes the positive electrode plate and the negative electrode plate. On the other hand, it is desirable to use the same component as a rectangular housing for containing the electrode body in consideration of reducing costs and improving efficiency of battery manufacturing.
Accordingly, some batteries are designed so that the thickness of the planar electrode body is smaller than the inside dimension of the rectangular housing, and such batteries have a gap between the rectangular housing and the electrode body. In such cases, it is desirable that a member be disposed in the gap so as to fill the gap with the member in order to prevent a gap from remaining between the rectangular housing and the electrode body. By doing so, movement of the electrode body in the housing can be suppressed. Moreover, because the rectangular housing can press against the electrode body, the positive electrode plate and the negative electrode plate can be prevented from becoming separated from each other, so that decreased battery performance due to separation of the electrode plates can be suppressed.
However, for example, the method of disposing the gap filling member on the inner surface of the insulation film, which is described in Patent Document 2, may cause the following problem. Typically, a rectangular secondary battery is made through the following process. First, an electrode body is connected to a current collector, which has been attached to a sealing plate together with a terminal. Next, the electrode body is wrapped in an insulation sheet and inserted into a rectangular housing. An opening in the rectangular housing is sealed by joining contact portions of the rectangular housing and the sealing plate to each other by laser welding or the like. Subsequently, a liquid electrolyte is injected through a liquid injection hole formed in the sealing plate, and the liquid injection hole is sealed with a sealing plug.
In the case where a gap filling member, which is independent from the insulation film, is disposed on an inner surface of the insulation film, when the liquid electrolyte is injected through the liquid injection hole formed in the sealing plate, part of the liquid electrolyte may flow into a space between the insulation film and the gap filling member. The part of the liquid electrolyte, which has flowed into the space between the insulation film and the gap filling member, may cause the insulation film and the gap filling member to stick to each other. If this occurs, the part of the liquid electrolyte does not flow out or does not easily flow out of the space between the insulation film and the gap filling member. The part of the liquid electrolyte, which does not flow out or does not easily flow out of the space between the insulation film and the gap filling member, is non-usable electrolyte, because it is not supplied to the electrode body. Accordingly, such a liquid electrolyte, if present, does not contribute to improving the performance of the battery and may only increase the weight of the battery.
Although the above problem may be a minor problem for a single rectangular secondary battery, the problem may become serious when a large number of rectangular secondary batteries are used in combination. In particular, this problem is significant for rectangular secondary batteries mounted on automobiles, because reduction in weight is very important for such batteries.